1. Field of the Invention
The invention relates to cementitious materials suitable for use as luting agents, sedative and insulating bases, temporary and long term restoratives, endodontic sealants, pulp capping materials, tissue packs, impression pastes and adhesives for dental composites and hard tissues. Specifically, the present invention relates to high strength, low solubility adhesives and restoratives containing vanillic acid esters and metal oxides which do not inhibit polymerization.
2. Description of the Prior Art
Oil of cloves has been used in the treatment of dental caries since the XVI century and its inclusion in combination with zinc oxide in dental cements, commonly referred to as luting agents, was reported over 100 years ago. Analysis revealed that oil of cloves contains approximately 85% by weight of eugenol. It is this latter compound which is used in zinc oxide-eugenol (hereinafter referred to as ZOE) dental cements. ZOE compositions have found wide application in dentistry including temporary restoratives, sedative bases, cementing media for crown and bridge work, in pulp capping, soft tissue packs in oral surgery and periodontics, root canal sealers in endodontics and with modifying agents as impression pastes.
ZOE cements possess much better biocompatibility than most other dental materials. They have excellent sealing characteristics and their bacteriocidal effectiveness has been well demonstrated. The cement acts as a palliative or anodyne and as a mild non-irritant antiseptic. Unfortunately, these materials have low strength, which may not be large enough to resist forces of mastication. Their lack of resistance to wear and disintegration, partially because of their high relative solubility in oral fluids of the mouth, further deters their more extensive use as temporary restorations or fillings. These materials also inhibit free radical polymerization because of the presence of an electron-rich phenolic hydroxyl group in the eugenol molecule. Thus, acrylic resins, and to a lesser extent composites, in contact with a ZOE cement do not polymerize completely. This incomplete cure results in polymer surface regions having poor physical properties such as low surface hardness. Furthermore, ZOE cements adhere only weakly to acrylic restorations, bone or dental tissues.
Although the eugenol ingredient is relatively non-toxic (LD.sub.50 of 0.5 g/kg for white mice), free eugenol has some inflammatory characteristics. Thus, when injected into the abdominal integument and eyes of rabbits, eugenol produces severe inflammation. It produces leucocytic infiltration and polymorphonuclear responses, and in direct contact with the pulp or periodontal tissues eugenol can act as a coagulent. In in vitro tests it shows a hemolyzing, protein precipitating action.
A further disadvantage is that eugenol has a penetrating long-lasting odor and lingering taste which can be unpleasant to many patients. In addition, incompletely hardened cements containing much residual eugenol can produce irritation and toxic cell reactions.
To overcome some of these deficiencies, especially to improve the mechanical strength of the ZOE cement, research has been directed to either replacing eugenol altogether with a more suitable substitute or towards including additives in the ZOE compositions which resolve many of the problems. However, the use of eugenol substitutes has usually resulted in cements possessing poor physical properties.
Zinc oxide will react with many chelate forming compounds, especially those containing o-methoxyphenol (guaiacol) groups to yield cementitious products. Cements obtained from o-ethoxybenzoic acid (referred to hereinafter as EBA) and zinc oxide have found a considerable number of applications in dentistry because of their strength and excellent biocompatibility, especially as luting agents and as bases. However, the materials still disintegrate too rapidly under clinical conditions to be employed for more permanent restorations.